This invention relates generally to the field of fittings which provide a passageway through a wall member for the passage of gases or other fluids, and more particularly to such fittings adapted for use with drums or other generally closed containers. Even more particularly, the invention relates to such fittings which include a selective filter in the passageway to prevent passage of certain matter. Still even more particularly, the invention relates to such fittings which allow for the passage of hydrogen gas but preclude the passage of radioactive particulates.
Hazardous wastes such as radioactive or chemical hazardous wastes, or in particular transuranic (TRU) wastes comprising radioactive elements, are currently typically disposed of by packing the wastes inside large drums, such as 55 gallon cylindrical plastic or metal drums, which are either closed in an air-tight manner such that no gases or other matter can escape from the containment, or are closed in a vented manner such that some gases are allowed to vent. In either case it is required that no radioactive material or substance can escape from the containment. The drums are then shipped to remote storage facilities for final storage, where they are stored underground or in specially designed structures. In many circumstances radiolysis (chemical decomposition brought about by radiation), chemical reactions or organic decomposition of the material placed within the drums creates hydrogen and/or other undesirable gases, resulting in a build-up over time of excessive amounts of hydrogen and/or other gases within the drum which if not addressed can lead to the formation of potentially explosive conditions. For example, it is potentially dangerous if the percentage of hydrogen gas exceeds five percent of the drum atmosphere. To address this serious problem, it is known to provide the storage drums with selective venting filters or other such devices which allow passage of hydrogen gases while retaining radioactive particulates within the drums. Unfortunately, many times the hazardous waste is first confined within inner layers of confinement, such as heat sealed, tied or knotted plastic bags made of relatively thin, flexible, relatively elastic, polyethylene (PE), polyurethane (PU) or polyvinyl chloride (PVC), cans or other rigid walled containers, or the like, which are then placed within the large drums, and a single drum will often contain multiple bags or other inner containers. Sometimes a quantity of hazardous waste is placed into two or more bags, with the first bag sealed and placed within the second, which is then sealed, etc. This results in an inner containment device with multiple layers of confinement. The drum itself forms the outer or primary layer of confinement and the inner containers form inner or secondary layers of confinement for the hazardous waste. Because the plastic bags and other inner containers are sealed and are by their nature impermeable to the gases which are formed over time, the gases are trapped and cannot pass through any venting devices provided for the drum, and undesirable or dangerous hydrogen gas build-up may occur within the drum.
In addition to the problem set forth above, some drums are provided with rigid internal polyethylene liners. In this case the drum forms the primary layer of confinement and the rigid internal liner forms a secondary containment layer.
Government transportation regulations promulgated by the Department of Energy, the Nuclear Regulatory Commission and other agencies require that where flexible inner layers of confinement are present within a drum, i.e., individual sealed bags or other containers, the amount of fissile hazardous material or the total waste wattage must be significantly limited in each drum. These regulations significantly increase shipping costs and require that excess amounts of fissile hazardous material or excess total waste wattage in a single drum must be repackaged into multiple drums. The current approach to this task involves opening the drums, physically breaching all the inner containers and then repackaging the containers within the drum or dispersing the containers into multiple drums. The bags cannot be merely punctured or slit, since the openings could be blocked upon repacking, resulting in entrapment of any new gases formed over time. Because of the hazardous nature of the materials involved, this process is extremely expensive due to the need to protect the workers from excessive exposure and due to the need to safely handle and isolate the hazardous materials from the environment during this operation, and costs for this type of operation can exceed $10,000 per drum. The amount of radioactive waste which can be put into a single drum having inner layers of confinement is severely restricted since if excess radioactive waste is stored in the drum, the drum will have to be opened and processed. For example, 20 grams of plutonium waste may be confined within a single drum under the guidelines where no inner containers are present, but only 2 grams of plutonium waste is allowed if there are inner containers. There are currently an estimated 800,000 drums containing radioactive TRU waste which require venting and subsequent storage. Current regulations preclude transport of the drums unless the drums contain less than five percent hydrogen gas.
It is an object of this invention to provide a filter vent fitting of novel structure for disposition on a drum, the filter vent allowing for the passage of certain fluids (gas or liquid) while preventing the passage of radioactive particles, which cooperates with means to safely breach the inner containment layers within a larger containment drum at relatively low cost, without requiring the opening of the drum and the handling and repackaging of the inner containers. It is a further object to provide a filter vent fitting which cooperates with such breaching means to perform this task in a manner which significantly reduces or removes worker exposure to the hazardous material, which can be performed at remote and various sites, which poses little or no threat for environmental release, which does not damage or degrade the drum, which does not cause chemical reactions within the drum, which functions on either PE, PU or PVC bags, which accounts for the problems created by rigid PE liners and sealed rigid-wall cans, and which breaches the inner containers in such manner that openings formed in the containers will not be blocked so that any gases which are produced over time subsequent to the initial venting and breaching operation will not be trapped by the inner containers but will vent in routine manner through venting devices. It is a further object to provide such a filter vent fitting which allows the interior of the drum to be evacuated or pressurized, and which allows liquid nitrogen or other cryogenic substance to be introduced into the drum to reduce the interior temperature. It is a further object to provide such a filter vent fitting which is self-drilling, self-tapping and self-sealing. It is a further object to provide such a filter vent fitting which also comprises pressure balancing means to maintain the pressure differential between the interior of the drum and the exterior of the drum disposed within a secondary chamber means within an acceptable pressure differential value.
The invention is a filter vent fitting adapted for use with drums or like closed containers to provide passageways through the wall or lid of the drum for selective passage of certain gases or liquids, while precluding passage of certain other substances, in particular radioactive particulates. The fitting is preferably self-drilling, self-tapping and self-sealing. The fitting comprises in general filter means which allows the passage of hydrogen and other gases while preventing the passage of radioactive particulates, such as a filter composed of sintered stainless steel, venting conduit means which allows gas produced within the drum to vent to the ambient and which allows gas to be introduced into or evacuated from the drum through said fitting in order to alter the interior pressure of the drum, and cryogenic/sampling conduit means which allows cryogenic substances, such as liquid nitrogen, to be introduced into the drum and gas samples to be extracted from the drum without passing through the filter media. The fitting is preferably provided with drilling means for breaching the lid of the drum, cutting means for creating an aperture in the drum lid to receive the fitting, fitting attachment means for securing the fitting to the drum, and sealing means to seal the junction between the fitting and the drum.
In a preferred embodiment, the fitting further comprises a cap member adapted to be secured to the fitting, with the cap member having evacuation/pressurization conduit means in fluid communication with the venting conduit means of the fitting, evacuation/pressurization connection means for joining the cap member to an evacuation or pressurization means, cryogenic/sampling conduit means in fluid communication with the cryogenic/sampling conduit means of the fitting, cryogenic/sampling connection means for joining the cap member to a cryogenic source or sampling means, and a pressure balancing bore in fluid communication with the evacuation/pressurization conduit means through which gases external to the fitting can be drawn during evacuation of the drum or through which pressurized gas can be expelled during pressurization of the drum. The volume of gases drawn into or expelled from the pressure balancing bore is a minor percentage of the total gas evacuated from or introduced into the drum.